A digital camera has an optical lens and an image sensor, which includes a plurality of pixel sensors. The optical lens is used for receiving light rays from an object that is placed in front of the camera. The optical lens allows the light rays to pass through the optical lens, for travelling to the image sensor.
Calibration parameters are used to describe characteristics of the camera. These calibration parameters comprise intrinsic parameters and extrinsic parameters.
The extrinsic parameters are used to define a translation and a rotation of a reference frame of the camera for aligning the location and the orientation of the camera reference frame with the location and the orientation of a known reference frame of the world. The world refers to an area, wherein the camera is located. Values of the extrinsic parameters change in accordance to a use or an application of the camera.
Referring to the intrinsic parameters, they act to link or map pixel coordinates of an image of the image sensor with corresponding coordinates of the camera reference frame. The coordinates often refer to a set of numbers for describing a position. In effect, the intrinsic parameters relate coordinates of light rays at the optical lens to corresponding coordinates of pixel sensor of the image sensor.
In a general sense, the light rays refer to electromagnetic radiation that can be visible or invisible. An example of the invisible light rays is infrared light rays.
These mapping between the pixel coordinates of the sensor image and the coordinates of the camera reference frame, which is defined by the intrinsic parameters, is often non-linear in a case when the camera optical lens is provided in the form of a wide-angle lens. The wide-angle lens is also called a fish-eye lens. The intrinsic parameters, which are defined in a factory that produced the camera, often have fixed values that are stored in a memory unit of the camera.
The intrinsic and extrinsic parameters are together used to relate a coordinate of a point in the world to a coordinate of a corresponding point in the image sensor of the camera.
It is desirable to present an improved method of determining calibration parameters of a camera. These calibration parameters comprise intrinsic parameters and extrinsic parameters and they are used to describe characteristics of the camera.